Pt and Pt–Ru nanoparticles decorated polypyrrole/multiwalled carbon nanotubes and their catalytic activity towards methanol oxidation

Conducting polymer composite films comprised of polypyrrole (PPy) and multiwalled carbon nanotubes (MWCNTs) [PPy–CNT] were synthesized by in situ polymerization of pyrrole on carbon nanotubes in 0.1 M HCl containing (NH₄)S₂O₈ as oxidizing agent over a temperature range of 0–5 °C. Pt nanoparticles are deposited on PPy–CNT composite films by chemical reduction of H₂PtCl₆ using HCHO as reducing agent at pH = 11 [Pt/PPy–CNT]. The presence of MWCNTs leads to higher activity, which might be due to the increase of electrochemically accessible surface areas, electronic conductivity and easier charge-transfer at polymer/electrolyte interfaces allowing higher dispersion and utilization of the deposited Pt nanoparticles. A comparative investigation was carried out using Pt–Ru nanoparticles decorated PPy–CNT composites. Cyclic voltammetry demonstrated that the synthesized Pt–Ru/PPy–CNT catalysts exhibited higher catalytic activity for methanol oxidation than Pt/PPy–CNT catalyst. Such kinds of Pt and Pt–Ru particles deposited on PPy–CNT composite polymer films exhibit excellent catalytic activity and stability towards methanol oxidation, which indicates that the composite films is more promising support material for fuel cell applications.     

Fabrication and catalytic properties of Pt and Ru decorated TiO2⧹CNTs catalyst for methanol electrooxidation

Highly ordered anodic titania nanotube arrays provide a large surface area for electrodepositing nickel nanoparticles which are used as the catalyst for carbon nanotube growth. Pt and Ru nanoparticles, approximately 3 nm in diameter, are uniformly electrodeposited on the as synthesized titania-supported carbon nanotubes (CNTs), constructing a novel catalyst for electrocatalytic oxidation of methanol. An enhanced and stable catalytic activity is obtained due to the uniformly dispersed Pt and Ru nanoparticles, and the large CNT network facilitating the electron transfer between the adsorbed methanol molecules and the catalyst substrate. An oxidation peak current density of 55 mA/cm² is achieved at a low Pt load of 0.126 mg/cm² with a Pt/Ru mole ratio of 1:1.     

Boron-doped diamond powder as catalyst support for fuel cell applications

The modification of boron-doped diamond powder with metallic oxides using the sol–gel method to prepare high area and very stable electrodes for the methanol oxidation reaction is reported here. The catalyst clusters thus prepared are irregularly distributed on the BDD powder surface having sizes varying between 500 nm and 5 μm and formed by the agglomeration of many nanoparticles. Electrochemical studies in acid media demonstrate that the deposited particles have a good electrical contact with the diamond powder surface and high purity. Moreover, the use of the sol–gel method on a BDD powder substrate leads to the formation of metallic and metallic oxides deposits of the desired composition. The electrocatalyst composite prepared in this manner (Pt–RuO_x/BDD powder) shows an excellent activity for methanol oxidation presenting an onset potential 20 mV lower than that observed on a Pt–Ru/C commercial catalyst, probably due to the ruthenium oxide contribution to the overall catalytic activity.     

Graphene supported electrocatalysts for methanol oxidation

Graphene nanosheet was prepared by modified Hummer’s chemical method and utilized as a catalyst support of PtRu nanoparticles for the electro-oxidation of methanol. Home-made graphene nanosheet was clearly characterized by Raman spectroscopy and we applied colloidal method to synthesize with high metal content of 80 wt.% Pt–Ru catalyst, which is extensively clarified by HR-TEM and XRD analysis. 80 wt.% Pt–Ru/graphene nanosheet catalyst showed superior electrochemical activity toward methanol oxidation compared to Pt–Ru/Vulcan XC-72R. It is due to the significant increase of electrochemical active surface area for better catalyst utilization.     

Pd/Pt core–shell nanowire arrays as highly effective electrocatalysts for methanol electrooxidation in direct methanol fuel cells

Highly ordered Pd/Pt–core–shell nanowire arrays (Pd/Pt NWAs) have been prepared by anodized aluminum oxide (AAO) template-electrodeposition and magnetron sputtering methods. Pd/Pt NWA electrode shows a very high electrochemical active surface area and high electrocatalytic activity for the methanol electrooxidation in acid medium for direct methanol fuel cells (DMFCs). The mass specific anodic peak current density is 756.7 mA mg⁻¹ Pt for the methanol oxidation on the Pd/Pt NWA electrode, an increase by a factor of four as compared to conventional E-TEK PtRu/C electrocatalysts. The mechanism of the significant enhancement of the Pd/Pt core/shell NWA nanostructure in the efficiency and electrocatalytic activity of Pt for the methanol electrooxidation in acid medium is discussed.     

Synthesis and electrochemical study of novel Pt-decorated Ti nanowires

We report on a facile approach to fabricate free-standing Ti nanowires and Pt-decorated Ti nanowires via a one-step environment-friendly and template-free process. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and energy dispersive X-ray (EDX) spectroscopy were employed to characterize the synthesized nanowires, showing that highly dense Ti nanowires with diameters of ～45 nm were directly grown on the Ti substrate and that the Pt nanoparticles coated onto the surface of Ti nanowires were uniform and ultrafine (～3 nm). Our electrochemical studies reveal that the active surface area of the Pt-decorated Ti nanowires is over 265 times larger than that of a polycrystalline Pt electrode and that the Pt-decorated Ti nanowires exhibit much higher activity for electrochemical oxidation of methanol compared to the polycrystalline Pt electrode.     

Amperometric biosensors based on deposition of gold and platinum nanoparticles on polyvinylferrocene modified electrode for xanthine detection

In this study, new xanthine biosensors, XO/Au/PVF/Pt and XO/Pt/PVF/Pt, based on electroless deposition of gold(Au) and platinum(Pt) nanoparticles on polyvinylferrocene(PVF) coated Pt electrode for detection of xanthine were presented. The amperometric responses of the enzyme electrodes were measured at the constant potential, which was due to the electrooxidation of enzymatically produced H₂O₂. Compared with XO/PVF/Pt electrode, XO/Au/PVF/Pt and XO/Pt/PVF/Pt exhibited excellent electrocatalytic activity towards the oxidation of the analyte. Effect of Au and Pt nanoparticles was investigated by monitoring the response currents at the different deposition times and the different concentrations of KAuCl₄ and PtBr₂. Under the optimal conditions, the calibration curves of XO/Au/PVF/Pt and XO/Pt/PVF/Pt were obtained over the range of 2.5 × 10^?3 to 0.56 mM and 2.0 × 10^?3 to 0.66 mM, respectively. The detection limits were 7.5 × 10^?4 mM for XO/Au/PVF/Pt and 6.0 × 10^?4 mM for XO/Pt/PVF/Pt. The effects of interferents, the operational and the storage stabilities of the biosensors and the applicabilities of the proposed biosensors to the drug samples analysis were also evaluated.     

Surface modified Pt/C as a methanol tolerant oxygen reduction catalyst for direct methanol fuel cells

A new procedure has been successfully developed by which PtN_x/C is synthesized to enhance methanol tolerance while maintaining a high catalytic activity for the oxygen-reduction reaction (ORR). The nitrogen-modified Pt surface, which is prepared using a chelating agent followed by heat treatment, exhibits considerable selectivity toward the ORR in the presence of methanol. The high methanol tolerance could be attributed to the suppression of methanol adsorption resulting from the modification of the Pt surface with nitrogen. A direct methanol fuel-cell (DMFC) test showed that a power density of up to 120 m W cm⁻² was generated when PtN_x/C was used as the cathode catalyst (1 mg cm⁻²) in 6 M methanol and oxygen at 70 °C.     

CO tolerant Pt/WC methanol electro-oxidation catalyst

Platinum supported on WC (Pt/WC) catalyst (20 wt.% Pt) was synthesized as a new methanol electro-oxidation catalyst. Particle size of 7.5 nm was obtained from X-ray diffraction results and a uniform distribution of particles was observed by transmission electron microscopy. In cyclic voltammetry (CV) measurement, the reduction peak potential of PtO increased from 0.72 V in commercial Pt/C to 0.76 V in Pt/WC. By combining the CV and CO stripping results, spill-over of H⁺ from Pt to WC was observed. Electrochemically active surface area calculated from the desorption area of H⁺ were 11.2 and 5.74 m²/g catalyst for Pt/WC and Pt/C, while those obtained from the desorption area of CO were 4.42 and 6.40 m²/g catalyst, respectively. CO electro-oxidation peak potential greatly decreased from 0.80 V in Pt/C to 0.68 V in Pt/WC. The reaction of WC with water to produce WC–OH could lower to CO electro-oxidation peak potential. Specific activity for methanol electro-oxidation increased from 144 mA/m² in Pt/C to 188 mA/m² in Pt/WC.     

Constructing a hierarchical graphene–carbon nanotube architecture for enhancing exposure of graphene and electrochemical activity of Pt nanoclusters

Stacking of individual graphene sheets (GS) is effectively inhibited by introducing one-dimensional carbon nanotubes to form a 3-D hierarchical structure which enhances the utilization of GS-based composites. From SEM images, CNTs are useful nanospacers for diminishing the face-to-face aggregation of GS. The specific electrochemically active surface area (SECSA) and specific double-layer capacitance (C_S,DL) of Pt/GS–CNTs (127.9 m²/g, 171.3 F/g) is much higher than that of Pt/GS (105.4 m²/g, 104.7 F/g) and Pt/CNTs (51.5 m²/g, 37.1 F/g), revealing the synergistic effects between GS and CNTs on enhancing the electrochemical activity of Pt nanoparticles and electrolyte-accessible surface area.     

Aqueous treatment of single-walled carbon nanotubes for preparation of Pt–Fe core–shell alloy using galvanic exchange reaction: Selective catalytic activity towards oxygen reduction over methanol oxidation

We have demonstrated a new, cost effective synthesis of single-walled carbon nanotube supported Pt–Fe core–shell alloy catalyst (Pt–Fe/SWNT) for the direct methanol fuel cell using galvanic exchange reaction. The Pt–Fe/SWNTs have shown much larger Pt active surface area (150 m²/g-Pt) than the commercial catalyst (54 m²/g-Pt). Furthermore, four-fold enhancement of catalytic activity of the Pt–Fe/SWNTs for oxygen reduction reaction (ORR) has been observed. This catalyst has also demonstrated its tolerance to methanol in ORR.     

A one-step,clean, capping-agent-free electrochemical approach to prepare Pt nanoparticles with preferential (100) orientation and their high electrocatalytic activities

A clean and simple electrodeposition method without the use of any organic additives has been reported to prepare platinum nanoparticles with preferential (100) orientation directly on the conductive substrate. The formation of platinum nanoparticles exposing (100) facets was confirmed by electrochemical methods and high-resolution transmission electron microscopy. The fraction of Pt (100) sites increases as the electrodeposition current density increases from 0.2 to 10 mA cm^− 2. Furthermore, as the Pt (100) fraction increases, the specific activity of the Pt particles for ammonia oxidation increases obviously.     

Performance of silver nanocubes based on electrochemical surface area for catalyzing oxygen reduction reaction

Ag nanocubes that are 45 nm in size are synthesized and successfully used as catalysts in oxygen electroreduction. Electrochemical surface areas (ESAs) are considered to determine the effect on HO₂⁻ production, which is found to be in the following order: nanocubes < nanoparticles. Comparative data generated using Tafel analyses in 0.1 M NaOH electrolyte without and with methanol show that unchanged slopes on the prepared cubic catalysts can indicate high resistance of Ag nanocubes for methanol oxidation during oxygen reduction reaction. Among these Ag catalysts, nanocubes exhibit 9.29 × 10^− 2 mA cm^− 2 (at − 0.15 V vs. Ag/AgCl), the better activity in the oxygen reduction reaction.     

High loading of Pt–Ru nanocatalysts by pentagon defects introduced in a bamboo-shaped carbon nanotube support for high performance anode of direct methanol fuel cells

Bamboo-shaped carbon nanotubes (BCNTs), with a large amount of pentagon defects introduced in the walls, were explored as the support of high loaded Pt–Ru catalysts for the anode of direct methanol fuel cells (DMFCs) in comparison with conventional carbon nanotubes (CNTs) and Vulcan XC carbon black. By ethylene glycol reduction, Pt–Ru catalysts with a high loading (60 wt%) and uniform particle size of 2–3 nm were uniformly deposited on BCNTs; while 60 wt% Pt–Ru catalysts on CNTs resulted in significant agglomeration. The Pt–Ru/BCNT catalyst showed the highest activity on methanol oxidation in cyclic voltammetry and highest performance as the anode in a DMFC single cell. Such an enhancement was largely ascribed to an enhanced interaction of the introduced pentagon defects with Pt–Ru, which could promote a high loading and well dispersion of Pt–Ru catalysts and the charge transfer from Pt–Ru to the tubes.     

Ultrasonic-electrodeposition of gold–platinum alloy nanoparticles on multi-walled carbon nanotubes – ionic liquid composite film and their electrocatalysis towards the oxidation of nitrite

We report here for the first time on the electrochemical co-deposition of gold–platinum (AuPt) nanoparticles on multi-walled carbon nanotubes (MWNT) – ionic liquid (i.e. trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl)imide, [P_6,6,6,14][NTf₂]) composite surface in ultrasonic field. The obtained AuPt nanoparticles were characterized by scanning electron microscope, X-ray diffraction and X-ray photoelectron spectroscopy. It was found that they were well-dispersed on the composite surface, with particle size about 10 nm. Furthermore, they exhibited alloy features. Electrochemical impedance spectroscopy and voltammetric experiments showed that the resulted AuPt-MWNT-[P_6,6,6,14][NTf₂] modified electrode possessed rather small electron transfer resistance and good catalytic activity towards nitrite oxidation. Under the optimized conditions, the oxidation current of nitrite was linear to its concentration in the range of 5–200 nM and the detection limit was down to 1.0 nM (S/N = 3).     

A novel route for preparation of PtRuMe (Me = Fe,Co, Ni) and their catalytic performance for methanol electrooxidation

PtRuMe (Me = Fe, Co, Ni) catalysts dispersed on multi-wall carbon nanotubes (MWCNTs) were prepared by ultrasonic-assisted chemical reduction. X-ray diffraction (XRD) showed that Pt existed as face-centered cubic structure, while Ru and Me alloyed with Pt. The calculated particle sizes from XRD data are of 3.40, 3.40, 2.61 and 3.06 nm for PtRu, PtRuFe, PtRuCo and PtRuNi, respectively, and are consistent with TEM results. The electrochemical measurements showed that the addition of Me to PtRu enhances the electrocatalytic properties for methanol oxidation and PtRuNi has the best catalytic activity and stability.     

Facile synthesis of PtRu/C electrocatalyst with high activity and high loading for passive direct methanol fuel cell by synergetic effect of ultrasonic radiation and mechanical stirring

The PtRu/C electrocatalyst with high loading (PtRu of 60 wt%) was prepared by synergetic effect of ultrasonic radiation and mechanical stirring. Physicochemical characterizations show that the size of PtRu particles of as-prepared PtRu/C catalyst is only several nanometers (2–4 nm), and the PtRu nanoparticles were homogeneously dispersed on carbon surface. Electrochemistry and single passive direct methanol fuel cell (DMFC) tests indicate that the as-prepared PtRu/C electrocatalyst possessed larger electrochemical active surface (EAS) area and enhanced electrocatalytic activity for methanol oxidation reaction (MOR). The enhancement could be attributed to the synergetic effect of ultrasound radiation and mechanical stirring, which can avoid excess concentration of partial solution and provide a uniform environment for the nucleation and growth of metal particles simultaneously hindering the agglomeration of PtRu particles on carbon surface.     

Synthesis of coin-like hollow carbon and performance as Pd catalyst support for methanol electrooxidation

The coin-like hollow carbon (CHC) has been synthesized by only using ethanol as the carbon source with a novel Mg/NiCl₂ catalytic system via a facile solvothermal method for the first time. The CHC synthesized at optimized conditions shows an average thickness of less than 154 nm and the coin diameter of 1–3 μm. The CHC is characterized by SEM, TEM, XRD and electrochemical techniques. Pd on CHC (denotes as Pd/CHC) electrocatalysts are prepared for methanol oxidation in alkaline media. The Pd/CHC electrocatalyst gives a mass activity of 2930 A g⁻¹ Pd for methanol oxidation against 870 A g⁻¹ Pd on Pd/C electrocatalyst. One main reason for the higher mass activity of the Pd/CHC is the higher electrochemical active surface area (EASA) of the Pd/CHC.     

Fabrication of the catalytic electrodes for methanol oxidation on electrospinning-derived carbon fibrous mats

The carbon fibrous mats with high conductivity (50 S cm⁻¹) formed by carbon nanofibers with an average diameter of ∼150 nm have been fabricated by thermally treating the electrospun polyacrylonitrile fibers. The platinum clusters are electrodeposited on the carbon nanofibrous mats (CFMs) by multi-cycle CV method. In contrast to the catalytic peak current of methanol oxidation on commercial catalyst (185 mA mg⁻¹ Pt), the catalytic peak current on optimum Pt/CFM electrode reaches to ∼420 mA mg⁻¹ Pt despite of the large size (50–200 nm) of the Pt clusters, revealing that the special structure of carbon fibrous mats is favorable to improve the performance of catalyst.     

Oxygen reduction activity dependence on the mesoporous structure of imprinted carbon supports

Two mesoporous carbons (with 15 (CIC-15) and 26 nm (CIC-26) diameter pores) were synthesized using a silica colloid imprinting method, loaded with 10 wt.% Pt, and then evaluated (against Vulcan^? carbon (VC)) as oxygen reduction (ORR) catalysts for use in proton exchange membrane fuel cells. Both Pt/CICs reproducibly out-performed Pt/VC, with Pt/CIC-15 demonstrating higher ORR activity than Pt/CIC-26, despite its smaller pore size and lower surface area. Transmission electron tomography showed that the Pt nanoparticles (4–5 nm diameter) are fully deposited throughout the pores of the CICs and that the pore distribution in CIC-26 is partially ordered, while CIC-15 shows no ordering of its pores. Importantly, using the powerful imaging capabilities of transmission electron tomography, a first-time correlation is demonstrated between the ORR activity and the wall thickness of the carbon support materials. Pt/CIC-15 has significantly thicker walls, giving a lower measured electronic resistance, a lower ORR Tafel slope, and thus better performance overall compared to Pt/CIC-26.